The long-term goal of this application is twofold: 1) to determine the PET and MRS characteristics of primary brain tumors in adults and to monitor the effects of therapy in these patients and 2) to determine in pediatric patients the role of PET and MRI with contrast in a) differentiating radiation necrosis from persistent/recurrent tumor and b) in determining which low-grade gliomas are more likely to disseminate. This application proposes to characterize blood flow, metabolism and MRS in untreated and recurrent brain tumors in adult patients. The effect of adenosine, which has been shown to increase tumor blood flow in experimental animals, will be determined. The effect of therapy on follow-up PET and MRS studies will be evaluated. The PET and MRS parameters prior to therapy and immediately after therapy will be evaluated to determine if these studies are predictive of tumor response (improved, stable, progressed). Two protocols involving pediatric brain tumors are to determine if FDG-PET studies are beneficial in patient management. The protocols evaluate the ability of PET to (1) differentiate radiation necrosis from tumor in patients having had hyperfractionation radiation therapy, and 2) predict which patients with supratentorial low-grade gliomas will develop CNS metastases. The results of these studies should provide an understanding of the role of PET and MRS in adults with previously untreated primary brain tumors and with recurrent tumor undergoing radiation and chemotherapy. Furthermore, the role of PET scanning in selected aspects of pediatric brain tumor management will be determined.